A photometer for measuring electromagnetic radiation absorption of a sample utilizing a source of the electromagnetic radiation. Electromagnetic radiation is conducted from the source, to a sample sensor or sensors, and is passed through or scattered from, the sample utilizing a sample cell. The electromagnetic radiation is then directed to a detection system which determines absorbance of electromagnetic radiation by the sample at the sample cell. The detection system includes a beam splitter which receives the electromagnetic radiation and outputs first and second beams. A first detector having a first wavelength filter and a second detector having a second wavelength filter receives the two beams from the splitters. One detector may be employed to produce a reference signal. The remaining detector or detectors produce an output signal which is a representation of a characteristic, such as absorbance of the sample. The output signals are compared to a reference signal, and converted into a measurement of absorbance, transmission, reflectance, or turbidity.